Manufacture of pigments



' sulfur or free selenium in Patented Dec. 22, 1942 S PATENT OFFlCEMANUFACTURE OF PIGMENTS Robert H. Long, Par-ma,

Harshaw Chemical Company, Elyria, Ohio, a

corporation of Ohio Ohio, assignor to The No Drawing. Application June28, 1940, Serial No. 342,921

Claims.

This invention relateslto the preparation of selenium and sulfurpigments, more particularly selenium red pigments, and has for itsobject to provide a process for the manufacture of such pigments ofsuperior brilliance and strength.

By selenium and sulfur pigments I mean pigments such as cadmiumsulfoselenides, cadmium sulfide, cadmopones' (CdS-BaSO or CdSSGrBaSOOzinc lithopones and the like, whether pure or containing diluents orfillers. By selenium red pigments I mean cadmium sulfoselenide pigmentsof the so-called C. P. type as well as those containing added orcoprecipitated fillersor extenders such as cadmium-selenium lithoponesand the like.

Prior to my invention the art has developed along the line of preventingthe presence of free these pigments by careful proportioning of theconstituents of the pigment batch and tying up the sulfur and seleniumin chemical combination before calcination.

These procedures are not entirely successful in the attainment'of theirobjective and sacrifice definite advantages otherwise obtainable in thecalcination of these pigments.

I have now discovered that superior pigments as respects brilliance andstrength can be produced if materials capable of yielding cadmium orzinc selenides, sulfides or sulfo-selenides, either I tracting agent andsuitable are alkali metal and ammonium monosulfides and of these Iprefer sodium monosulfide.

A wide variation in the relative amounts of exwater are possible, forexample, from a solution of NazS to a saturated solution thereof at theboiling point. I prefer a 4% to 8% solution as a practical range, strongenough for good results but notstrong enough to render the processunduly expensive. Usually 5 to '10 pounds of extracting agent per 100pounds of pigment will be found suitable. The quantity of extractingagent is, of course, more properly related to the amount of selenium orsulfur to be extracted. I prefer to usea minimum of /4 pound of NazS foreach pound of free selenium in the pigment. This quantity wouldapproximate the theoretica. minimum assuming that NazS dissolvesselenium as NazSSei. Practically, a small amount of selenium mightremain, but very marked improvement would result in a case where thepigment contained any considerable quantity of free selenium. I prefernot to use more than 12 pounds of NazS per pound of selenium in thepigment. A greater quantity would, no doubt, be effective but hardlynecessary in any case. In the case of sulfur, about /2 Pound of NazS perpound of sulfur in the pigment is a practical minimum, while hardly morethan pounds should be found necessary. The extracpure or admixed withadded or co-precipitated diluents, are calcined in an atmosphere ofselenium in the case of selenide pigments or sulfur in the case ofsulfide pigments or selenium or sulfur and selenium in the case ofsulfo-selenide pigments, all in substantial absence of oxygen, and thenthe free selenium or free sulfur are extracted by the use of an alkalinesolvent inert to the pigments. I am aware that pigments. of this classcan tolerate a small quantity of free selenium or sulfur or both, butclose control of the quantity of free selenium or sulfur is desirable ifcolor and strength are to be reproduced from batch to batch. Less closecontrol is necessary when the extracting step herein described isemployed.

Suitable solvents are alkali metal, barium, strontium and ammoniummonosulfides, polysultides, monoselenides and hydrosulfides, and alkalimetal and ammonium hydroxides, normal carbonates and sulfites. Otheralkaline solvents inert to the pigments may be used for extracting thefree selenium or sulfur. Many of these solvents are relatively lessdesirable than others on account of cost. The solvents which tion may becarried out at any temperature between the freezing -point and theboiling point of the solution, but temperatures between 20 C. and 80 C.are preferred.

Potassium sulfides may be substituted for sodium sulfides in molecularlyequivalent quantities and with similar results. Ammonium sulfide shouldbe employed in larger than molecularly equivalent quantities. Apparentlythe concentrations of ammonium sulfide and other alkaline solvents mostdesirable are those required to produce pH values equivalent to thoseproduced by quantities of NazS within the above indicated range.However, it cannot be said that all the various alkaline solvents havethe same solvent power.- Some are weaker than others, possibly becauseof a different dissolving mechanism. It is my belief, for example, thatNaOH dissolves selenium by forming first NazSe which then takes up moreselenium by forming the polyselemde.

Sodium mono-sulfide-appears to be the most desirable extracting agent orsolvent on account of its highelfectiveness and low cost. The alkalimetal and ammonium mono-sulfides constitute a sub-group of extractingagents of outstanding I find most value for my purpose.

Eaample pigment comprising preparing a suitable pigment Approximately120 parts by weight of a pigthe pmquction of Such pigment ment batchcontaining ingredients suitable for cmmg Sal-d batFh m an atmosphere ofselenium the production of a cadmium suli'o-selenide plg- Vapor.substamtany free f oxygen whereby ment were calcined in a seleniumvapor atmos- 5 h 15 produced. a se]en mm red pigment phere at 6509 C for1/2) hour and immediately taming free selenium derived from thecalcinaquenched in Water. The calcined material coni t and subJectingsaid pigment to tamed o t /2 parts by weight of free se1e iltlltlOIlintan aqueous selenium solvent inert to v v e pigmen i g g g g gf fi 23525 zfg 3 52335 10 3. A process for production of a. selenium redWeight of sodium mono-sulfide. The temperature pigment comprising F asultajble pigment approximately 3 R and the time of ban batch for theproduction of such pigment, calmilling 30 minutes. The content of theball mill mung 531d bat9h an atmosphere Selenium was filtered and washedwith water and found to Vapor substantially free from oxygen wherebycontain substantially no free selenium and to be 15 ther? is produced aSelenium red pigment 1 i rov rilliance and stren th. l-5533:; a l}; desiri bed my invention, what I of 1%% of the pigment batch and thenremov' claim ing such free selenium from the pigment by ex- A process fthe production of a selenium traction with an aqueous solvent forselenium red pigment comprising calcining the pigment 29 which SOIVPnt15111811; to the pigment. batch in an atmosphere of selenium vapor sub-A Process according o c im 1 f rther charstantially free from oxygen andthen extracting acterl'zed in that during the extraction e MB- "freeselenium from the resulting pigment by the merit Subjected to attrition.use of an aqueous solution of a substance of the 5. A pro s according tcla m 1 further charclass consisting of alkali metal, barium, t 25acterized in that the quantity of free selenium in tium, and ammoniummonosulfides polysulfides, the pigment be ore e tractio s approximatelymonoselenides, and hydrosuifides, and alkali such as results fromcalcination in an atmosphere metal and ammonium hydroxides. normal carofselenium vapor. bonates and sulfites. ROBERT H. LONG;

2. A process for production of a selenium red

